Power and data transfer in hearing prostheses

ABSTRACT

Embodiments presented herein are generally directed to techniques for separately transferring power and data from an external device to an implantable component of a partially or fully implantable medical device. The separated power and data transfer techniques use a single external coil and a single implantable coil. The external coil is part of an external resonant circuit, while the implantable coil is part of an implantable resonant circuit. The external coil is configured to transcutaneously transfer power and data to the implantable coil using separate (different) power and data time slots. At least one of the external or internal resonant circuit is substantially more damped during the data time slot than during the power time slot.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Non-Provisionalapplication Ser. No. 15/593,576 entitled “Power and Data Transfer inHearing Prostheses,” filed May 12, 2017, which is a continuationapplication of U.S. Non-Provisional application Ser. No. 14/542,877entitled “Power and Data Transfer in Hearing Prostheses,” filed Nov. 17,2014, which in turn claims priority to U.S. Provisional Application No.61/933,512 entitled “Power and Data Transfer in Hearing Prostheses,”filed Jan. 30, 2014, the entire contents of which are herebyincorporated by reference.

BACKGROUND Field of the Invention

The present invention relates generally to hearing prostheses, and moreparticularly, to power and data transfer in hearing prostheses.

Related Art

Medical devices having one or more implantable components, generallyreferred to herein as implantable medical devices, have provided a widerange of therapeutic benefits to recipients over recent decades. Inparticular, partially or fully-implantable medical devices such ashearing prostheses (e.g., bone conduction devices, mechanicalstimulators, cochlear implants, etc.), implantable pacemakers,defibrillators, functional electrical stimulation devices, and otherimplantable medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions for a number of years.

The types of implantable medical devices and the ranges of functionsperformed thereby have increased over the years. For example, manyimplantable medical devices now often include one or more instruments,apparatus, sensors, processors, controllers or other functionalmechanical or electrical components that are permanently or temporarilyimplanted in a recipient. These functional components perform diagnosis,prevention, monitoring, treatment or management of a disease or injuryor symptom thereof, or to investigate, replace or modify of the anatomyor of a physiological process. Many of these functional componentsutilize power and/or data received from external components that arepart of, or operate in conjunction with, the implantable medical device.

SUMMARY

In one aspect presented herein, an implantable medical device isprovided. The implantable medical device comprises an implantableresonant circuit comprising an implantable coil, and an externalresonant circuit comprising an external coil configured totranscutaneously transfer power and data to the implantable coil usingseparate power and data time slots. At least one of the external orimplantable resonant circuit is substantially more damped during thedata time slots than during the power time slots.

In another aspect presented herein, an external transmitter circuit isprovided. The external transmitter circuit comprises an externalresonant circuit comprising an external coil and one or more driverbridges configured to cause the external coil to transfer power and datato an implantable receiver circuit using separate power and data timeslots. The quality factor of the external resonant circuit is lowerduring the data slots than during the power time slots.

In another aspect presented herein, an apparatus is provided. Theapparatus comprises an implantable resonant circuit comprising animplantable coil, an external resonantcircuit comprising an externalcoil forming a transcutaneous power and data link with the implantablecoil, and at least one driver bridge configured to drive the externalcoil so as to separately transfer power and data to the implantablecoil. Operational characteristics of at least one of the implantableresonant circuit or the external resonant circuit are dynamicallyadjusted during transfer of data to the implantable coil.

In another aspect presented herein, a method for transmitting power froman external transmitter circuit to an implantable receiver circuit isprovided. The external transmitter circuit comprises an externalresonant circuit that includes an external coil, while the implantablereceiver circuit comprise an implantable resonant circuit that includesan implantable coil. The method comprises driving the external resonantcircuit with one or more driver bridges during a power time slot tocause the external coil to transfer power to the implantable receivercircuit. The method further comprises driving the external resonantcircuit with one or more driver bridges during a data time slot to causethe external coil to transfer data to the implantable receiver circuit.The power and data time slots are different time slots and the externalresonant circuit is driven such that the quality factor of the externalresonant circuit is lower during the data slot than during the powertime slot.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates an implantable hearing prostheses configured toimplement separated power and data transfer techniques in accordancewith embodiments presented herein;

FIG. 2A is a simplified schematic diagram of an external transmittercircuit configured to implement separated power and data transfertechniques in accordance with embodiments presented herein;

FIG. 2B is a timing diagram illustrating signals supplied to theexternal transmitter circuit of FIG. 2A;

FIG. 3 is a simplified schematic diagram of an external transmittercircuit and an implantable receiver circuit each configured to implementseparated power and data transfer techniques in accordance withembodiments presented herein;

FIG. 4 is a timing diagram illustrating signals observed at theimplantable receiver circuit of FIG. 3 during the separated power anddata transfer techniques;

FIG. 5 is a simplified schematic diagram of another external transmittercircuit configured to implement separated power and data transfertechniques in accordance with embodiments presented herein;

FIG. 6 is a simplified schematic diagram of another external transmittercircuit configured to implement separated power and data transfertechniques in accordance with embodiments presented herein; and

FIG. 7 is a simplified schematic diagram of an implantable receivercircuit configured to implement separated power and data transfertechniques in accordance with embodiments presented herein.

DETAILED DESCRIPTION

Embodiments presented herein are generally directed to techniques forseparately transferring power and data from an external device to animplantable component of a partially or fully implantable medicaldevice. The separated power and data transfer techniques use a singleexternal coil and a single implantable coil. The external coil is partof an external resonant circuit, while the implantable coil is part ofan implantable resonant circuit. The external coil is configured totranscutaneously transfer power and data to the implantable coil usingseparate (different) power and data time slots. At least one of theexternal or internal resonant circuit is substantially more dampedduring the data time slot than during the power time slot. In certainembodiments, the external and internal resonant circuits are resonsanttank circuits.

Embodiments of the present invention are described herein primarily inconnection with one type of implantable medical devices, namelypartially implantable hearing prostheses comprising an externalcomponent and an internal (implantable component). Hearing prosthesesinclude, but are not limited to, auditory brain stimulators, cochlearimplants (also commonly referred to as cochlear implant devices,cochlear prostheses, and the like; simply “cochlear implants” herein),bone conduction devices, and mechanical stimulators. It is to beappreciated that embodiments of the present invention may be implementedin any partially or fully implantable medical device now known or laterdeveloped.

FIG. 1 is a perspective view of an exemplary cochlear implant 100configured to implement separated power and data transfer techniques inaccordance with embodiments presented herein. The cochlear implant 100includes an external component 142 and an internal or implantablecomponent 144. The external component 142 is directly or indirectlyattached to the body of the recipient and typically comprises one ormore sound input elements 124 (e.g., microphones, telecoils, etc.) fordetecting sound, a sound processor 134, a power source (not shown), anexternal coil 130 and, generally, a magnet (not shown) fixed relative tothe external coil 130. The sound processor 134 processes electricalsignals generated by a sound input element 124 that is positioned, inthe depicted embodiment, by auricle 110 of the recipient. The soundprocessor 134 provides the processed signals to a transmitter circuitconfigured to drive (activate) external coil 130.

As used herein, an “external component” refers to one or more elementsor devices that are part of, or operate in conjunction with, theimplantable medical device. In other words, an external component mayform part of the implantable medical device or may be a separate devicethat operates with an implantable medical device.

Returning to the example of FIG. 1, the implantable component 144comprises an implant body 105, a lead region 108, and an elongatestimulating assembly 118. The implant body 105 comprises a stimulatorunit 120, an implantable (internal) coil 136, and an internalreceiver/transceiver unit 132, sometimes referred to herein astransceiver unit 132. The transceiver unit 132 is connected to theinternal coil 136 and, generally, a magnet (not shown) fixed relative tothe internal coil 136. Internal transceiver unit 132 and stimulator unit120 are sometimes collectively referred to herein as astimulator/transceiver unit 120.

Implantable coil 136 is typically a wire antenna coil comprised ofmultiple turns of electrically insulated single-strand or multi-strandplatinum or gold wire. The electrical insulation of implantable coil 136is provided by a flexible silicone molding. In use, transceiver unit 132may be positioned in a recess of the temporal bone of the recipient.

The magnets in the external component 142 and implantable component 144facilitate the operational alignment of the external coil 130 with theimplantable coil 136. The operational alignment of the coils enables theexternal coil 130 to transmit/receive power and data to the implantablecoil 136. As described further below, the external component 142 isconfigured to transmit electrical signals (i.e., power and data) fromexternal coil 130 to implantable coil 136 using separate time slots overa radio frequency (RF) link.

Elongate stimulating assembly 118 is implanted in cochlea 140 andincludes a contact array 146 comprising a plurality of stimulatingcontacts 148. Stimulating assembly 118 extends through cochleostomy 122and has a proximal end connected to stimulator unit 120 via lead region108 that extends through mastoid bone 119. Lead region 108 couples thestimulating assembly 118 to implant body 105 and, more particularly,stimulator/transceiver unit 120. The stimulating contacts 148 may beelectrical contacts, optical contacts, or a combination of optical andelectrical contacts.

As noted above, a transcutaneous RF link is provided to transfer powerand data from external component 142 to implantable component 144.Certain conventional transcutaneous RF links use an amplitude modulatedsignal where the data and the power are transferred simultaneously(i.e., at the same time) over the same RF coil for extraction by theimplantable component. In other words, the data signals are embedded inthe power signals for simultaneous transmission from the external coilto the implantable coil. RF links that simultaneously transmit power anddata are sometimes referred to as combined power and data links.

Other conventional arrangements use time multiplexing of pure power anddata signals on separate RF links from different power and datatransmitters. More specifically, in such arrangements a first RF link iscreated between a first external coil and an implantable coil. Thisfirst RF link is used solely for data transmission. Additionally, asecond RF link is created between a second (different) external coil andthe implantable coil. This second RF link is used solely for powertransmission. A time multiplexing scheme is implemented such that eitherthe first RF link or the second RF link is activated and at one time inorder to avoid interference between the power and data signals. In otherwords, these arrangements use a first RF link (and first external coil)that is dedicated to data transmission and a second RF link (and secondexternal coil) that is dedicated to power transmission where the firstand second links are alternatively activated.

Presented herein are separated power and data transfer techniques inwhich a single transcutaneous RF link is used to separately transferpower and data from an external component to an implantable component.In accordance with the separated power and data transfer techniques,transfer of power and data occur during separate (different) time slotsusing the same external coil 130 (i.e., a shared external coil for bothdata and power). For example, a single transmission sequence/frame maybe split into a power time slot (block) and a data time slot (block) andrepeated. All of the power towards the implantable component 144 istransferred during the power time slot.

In order to enable use of a single shared external coil for power anddata transmission during different time slots, the operationalcharacteristics of one or both of an external transmitter (ortransceiver) or an implantable receiver (or transceiver) are dynamicallyadjusted between the power and data slots. More specifically, theimplantable receiver includes an implantable resonant circuit (e.g., animplantable resonant tank circuit) comprising an implantable coil, whilethe external transmitter includes an external resonant circuit (e.g., anexternal resonant tank circuit) comprising an external coil configuredto transcutaneously transfer power and data to the implantable coilusing the separate power and data time slots. At least one of theexternal or internal resonant circuit is substantially more dampedduring the data time slot than during the power time slot. That is, thequality factor (Q) of one or both of the external circuit or theinternal resonant circuit is reduced during data transmission (relativeto the quality factor of one or both of the external circuit or theinternal resonant circuit during power transmission).

For ease of illustrations, embodiments will be primarily describedherein with reference to the use of external and implantable resonsanttank circuits. It is to be appreciated that embodiments may includeother types of external and/or implantable resonant circuits.

As noted, the techniques presented herein involve switching betweenpower transfer for some fraction of the frame, and then data transferfor another part of the frame. By decoupling the data from the power,the RF link can be optimized for efficient power transfer during thepower time slots and then independently optimized for data transfer. Forexample, a very high quality factor may be used to optimize the powertransfer efficiency during the power time slots. However, when switchingto the data transfer mode, the internal or external tank circuit isdampened (and optionally detuned) to improve data integrity.

FIG. 2A is a schematic diagram illustrating a transmitter circuit 220configured to separately transfer power and data signals from anexternal component of an implantable component via a single externalcoil 222. In the embodiment of FIG. 2A, the external coil 222 is part ofan external resonant tank circuit 225 that also comprises capacitor 242(capacitor C1) and capacitor 244 (capacitor C2). In practice, externalcoil 222 has an inductive component (L_(HPC)) 246 and some small copperlosses represented as the series resistive component (R_(HPC)) 248.

The transmitter circuit 220 comprises a driver bridge 240. In certainembodiments, the driver bridge 240 is a full H-bridge driver. In otherembodiments, the driver bridge 240 is a half H-bridge driver. The driverbridge 240 includes an input 250 that receives an input signal 231 (FIG.2B) via a data input line 252. The driver bridge 240 also comprises afirst output 254 and a second output 256 (differential output). Thefirst output 254 is connected to capacitor 242 (which is connected toexternal coil 222) via a series circuit 257. The series circuit 257comprises a resistor 258 (R1) in series with an inductor 260 (L1). Thesecond output 256 is connected to capacitor 244 (which is also connectedto external coil 222) via a series circuit 261. The series circuit 261comprises resistor 262 (R2) in series with an inductor 264 (L2). In analternative arrangement the driver may only contain a single output(Half H-bridge or single push-pull) connected to a single series circuitcomprising a resistor (R1) in series with an inductor 260 (L1).

The first output 254 and the second output 256 of driver bridge 240 arealso connected to the capacitors 242 and 244, respectively, via a switch266. When the switch 266 is closed, the first output 254 is directlyconnected to capacitor 242 so as to bypass series circuit 257 (i.e.,bypass resistor 258 and inductor 260). Similarly, when the switch 266 isclosed, the second output 256 is directly connected to capacitor 244 soas to bypass series circuit 261 (i.e., bypass resistor 262 and inductor264). The switch 266 may be closed in response to an enable power signal233 (FIG. 2B) received via enable power line 268.

As noted above, power and data are transmitted during non-overlappingand separate (i.e., different) time slots. FIG. 2B illustrates a powertime slot 235 and a data time slot 237 where On-Off keying (OOK) is usedto transmit both the power and the data. In OOK, the signal may beeither a “1” (i.e., a pulse of energy is present) or a “0” (i.e., nopulse of energy is present). In certain examples, five (5) cycles orpulses may represent a ‘1’ cell and the absence of energy during five(5) cycles may represent a ‘0’ cell. Energy is taken from the ‘1’ cells.As shown in FIG. 2B, during the power time slot 235, the input signal231 is all ‘is,’ but switches between ‘1s’ and ‘0s’ during the data timeslot 237. The switching between 1s' and ‘0s’ during the data time slot237 is a digital code that is decoded at the implantable component.

The enable power signal 233 is a pulse waveform that also alternativesbetween a value of ‘1’ and ‘0.’ During the power time slot 235, theenable power signal 233 has a value of ‘1’ so as to close the switch266. This causes the outputs 254 and 256 of the driver bridge 240 to bedirectly connected to the capacitors 242 and 244, respectively, so as tobypass the series circuits 257 (R1 and L1) and 261 (R2 and L2).

Assuming for ease of illustration that the driver bridge 240 and theswitch 266 are ideal, the resonance frequency of the external resonanttank circuit 225 during the power time slot (f_(res_power_timeslot)) isdefined below in Equation 1.

$\begin{matrix}{f_{{{res}\_ {power}}{\_ {timeslot}}} = \frac{1}{2\pi \sqrt{L_{HPC}.\left( \frac{C\; 1.C\; 2}{{C\; 1} + {C\; 2}} \right)}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In the arrangement where the switch 266 is closed, the quality factor(Q) of the resonant tank circuit 225 during the power time slot(Q_(ext_power_timeslot)) is defined below in Equation 2.

$\begin{matrix}{Q_{{{ext}\_ {power}}{\_ {timeslot}}} = \frac{\omega \; L\; 3}{R_{HPC}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

wherein ω=2πf≈2πf_(res)

Maximum power efficiency is obtained when the quality factor of theexternal resonant tank circuit 225 during the power time slot ismaximized or R_(HPC) is minimized. In order to maximum the qualityfactor of the external tank circuit during power transfer, the switch266 is closed during the power time slots 235 so that signals providedby driver bridge 240 bypass the series circuits 257 (R1 and L1) and 261(R2 and L2), thereby ensuring that the quality factor and of theexternal resonant tank circuit 225 is not affected (reduced) by theseries circuits 257 and 261.

Additionally, the external coil current is maximized when the resonantfrequency of the resonant tank circuit 225 during the power time slot issubstantially equal or close to the operating frequency (f₀) of theexternal coil 222 (i.e., drive more current through the external coilwhile maintaining the driver at the same voltage). Therefore, thefrequency of the external resonant tank circuit 225 is set (via tuningof capacitors 242 and 244) to be close or equal to the operatingfrequency to maximize the power efficiency of the transcutaneous link.During the transcutaneous power transfer, the closure of the switch 266during the power time slots 235 (so that signals provided by driverbridge 240 bypass the series circuits 257 (R1 and L1) and 261 (R2 andL2) ensures that the resonant frequency of the external resonant tankcircuit 225 is not affected by the series circuits 257 and 261.

During the data time slots, the switch 266 is opened so that the seriescircuits 257 (R1 and L1) and 261 (R2 and L2) are placed in seriesbetween the driver bridge 240 and the external coil 222. Placing theseries circuits 257 and 261 between the driver bridge 240 and theexternal coil 222 causes a drop in the quality factor of the resonanttank circuit 225, the external coil current, and the resonancefrequency. In this case, the resonance frequency of the externalresonant tank circuit 225 during the data time slot(f_(res_data_timeslot)) is defined below in Equation 4.

$\begin{matrix}{f_{{{res}\_ {data}}{\_ {timeslot}}} = \frac{1}{2\pi \sqrt{\left( {L_{HPC} + {L\; 1} + {L\; 2}} \right).\left( \frac{C\; 1.C\; 2}{{C\; 1} + {C\; 2}} \right)}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Additionally, in the arrangement where the switch 266 is open, thequality factor of the resonant tank circuit 225 during the data timeslot (Q_(ext_data_timeslot)) is defined below in Equation 5.

$\begin{matrix}{Q_{{{ext}\_ {data}}{\_ {timeslo}t}} = \frac{\omega.\left( {{L\; 3} + {L\; 1} + {L\; 2}} \right)}{R_{HPC} + {R\; 1} + {R\; 2}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

wherein ω=2πf≈2πf_(res)

It has been discovered that the data integrity improves when theexternal resonant tank circuit 225 is more dampened (i.e., has a lowerquality factor) during data transmission. This is opposed to powertransmission where, as noted above, maximum power efficiency is achievedwhen the quality factor of the resonant tank circuit is maximized. Assuch, in accordance with the techniques presented herein, the qualityfactor of the resonant tank circuit is maximized during powertransmission, but is purposely lowered during data transmission (i.e.,Q_(est_data_timeslot)<Q_(ext_power_timeslot)). The dampened externalresonant tank circuit 225 reduces the ringing effects during one or more‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOKmodulation at f₀. The series resistors 258 and 262 operate to dampen theexternal resonant tank circuit 225 when connected in series between thebetween the driver bridge 240 and the external coil 222.

It has also been discovered that the data integrity improves and thatthe external coil current drops during the data time slot when theexternal resonant tank circuit 225 is tuned lower than the operatingfrequency. The lower the tuning frequency of the external coil 222 isrelative to the operating frequency, the higher the decrease in currentflow through the external coil 222 when the driver bridge 222 is actingas a pulsating voltage source (e.g. Class-D driver bridge). As describedfurther below, the decrease in the external coil current preventsinterference of the implantable component load with the data recovery atthe implantable component. In one example, the operating frequency ofthe external coil 222 is 5 megahertz (MHz) and the resonant frequency ofthe external resonant tank circuit 225 during data transmission(f_(res_data_timeslot)) is set equal to 4.75 MHz). The series inductors260 and 264 operate to reduce the resonant frequency of the externalresonant tank circuit 225 when connected in series between the betweenthe driver bridge 240 and the external coil 222.

As shown in FIG. 2A, the resonance frequency and quality factor duringthe power time slot and the data time slot are dynamically adjustedthrough the use of the switch 266. FIG. 3 illustrates an alternativearrangement where a dedicated driver bridge, rather than a switch, isused to dynamically adjust the resonance frequency and quality factor ofan external tank circuit.

More specifically, FIG. 3 is a schematic diagram illustrating anexternal transmitter circuit 320 configured to separately transfer powerand data signals to an implantable component via a single external coil322. In the embodiment of FIG. 3, the external transmitter circuit 320comprises a first driver bridge 340 (data driver bridge) and a seconddriver bridge 341 (power driver bridge). As described further below, thedriver bridge 340 is enabled during the data time slot, but isdeactivated during the power time slot. Similarly, the driver bridge 341is enabled during the power time slot, but is deactivated during thedata time slot. As such, the arrangement of FIG. 3 uses dedicated driverbridges for each of data and power transmission (i.e., the data andpower signals have their own driver bridges and only a single driverbridge is enabled at a time).

In the embodiment of FIG. 3, the external coil 322 is part of anexternal resonant tank circuit 325 that also comprises capacitor 342(capacitor C1) and capacitor 344 (capacitor C2). In practice, externalcoil 322 has an inductive component (L_(HPC)) 346 and some small copperlosses represented as the series resistive component (R_(HPC)) 348.

The driver bridge 340 includes an input 350 that receives an inputsignal 331 via data input line 352 and an enable data input 353 thatreceives a enable data signal 329 via enable data signal line 355. Thedriver bridge 340 also comprises a first output 354 and a second output356. The first output 354 is connected to capacitor 342 (which isconnected to external coil 322) via a series circuit 357 that comprisesa resistor 358 (R1) in series with an inductor 360 (L1). The secondoutput 356 is connected to capacitor 344 (which is also connected toexternal coil 322) via a series circuit 361 that comprises resistor 362(R2) in series with an inductor 364 (L2).

The driver bridge 341 includes an input 369 that receives a power signal327 via power input line 372 and an enable power input 373 configured toreceive an enable power signal 327 via enable power signal line 375. Thedriver bridge 341 also comprises a first output 374 and a second output376. The first output 374 is directly connected to capacitor 342 (whichis connected to external coil 322) so as to bypass series circuit 357.Similarly, the second output 376 is directly connected to capacitor 344so as to bypass series circuit 361.

The power signal 327 is a series of all ‘1’ values (consecutive powercycles), while the data input signal 331 switches between ‘1s’ and ‘0s’(i.e., at 5 MHz a ‘1’ represents five (5) cycles or pulses during 1 μsand a ‘0’ represents a silence during 1 μs for a data rate of 1 Mbps).The enable power signal 333 is a logic signal that alternatives betweena value of ‘1’ and ‘0.’ The enable data signal 329 is also a pulsewaveform that alternatives between a value of ‘1’ and ‘0.’ The enablesignal activates the respective driver at value ‘1’. However, the enabledata signal 329 is the inverse of the enable power signal 333 (note WME:make this more visible in FIG. 3). That is, when the enable power signal333 is ‘1’, the enable data signal 329 is a ‘0’ value, and vice versa.

In the embodiment of FIG. 3, power and data are transmitted duringnon-overlapping and separate (i.e., different) time slots using theseparate driver bridges. During the data time slots, the enable datasignal 329 is high so as to enable driver bridge 340. As such, theoutputs 354 and 356, generated using data input signal 331, are used todrive external coil 322. At the same time, the enable power signal 333is low so as to cause the outputs 374 and 376 of driver bridge 341 to beplaced in a high impedance state.

As noted above, the first output 354 is connected to external coil 322via series circuit 357 (R1 and L1) and the second output 356 isconnected to external coil 322 via series circuit 361 (R2 and L2). Assuch, when driver bridge 340 is enabled, the external coil 322 is drivenwith signals that pass through series circuit 357 and series circuit361.

During the power time slots, the enable power signal 333 is high (i.e.,a ‘1’ value) so as to enable driver bridge 341. As such, the outputs 374and 376, generated using power signal 327, are used to drive externalcoil 322. At the same time, the enable data signal 329 is low (i.e., a‘0’ value) so as to cause the outputs 354 and 356 of driver bridge 340to be placed in a high impedance state.

As noted, maximum power efficiency is obtained when the quality factorof the external resonant tank circuit 325 during the power time slot ismaximized or R_(HPC) is minimized. Additionally, the external coilcurrent is maximized when the resonant frequency of the resonant tankcircuit 325 during the power time slot is substantially equal or closeto the operating frequency (f₀) of the external coil 322. Therefore,during the power time slots, the bridge 341 is enabled to drive theexternal coil 322 with signals that pass directly from the outputs 374and 376 to capacitors 342 and 344, respectively. In this arrangement,the signals bypass the series circuits 357 (R1 and L1) and 361 (R2 andL2), thereby ensuring that the quality factor and resonant frequency ofthe external resonant tank circuit 325 are not affected by the seriescircuits 357 and 361.

However, also as noted above, the data integrity improves when theexternal resonant tank circuit 325 is more dampened (i.e., has a lowerquality factor) during data transmission. As such, during the data timeslots, the driver bridge 340 is enabled so as to drive external coil 322with signals that pass through the series circuit 357 (R1 and L1) andseries circuit 361 (R2 and L2). That is, the series circuit 357 (R1 andL1) and series circuit 361 (R2 and L2) are placed in between the driverbridge 340 and the external coil 322. Driving the external coil 322 viathe series circuits 357 and 361 causes a drop in the quality factor ofthe resonant tank circuit 325, the external coil current, and theresonance frequency of the resonant tank circuit. It should be notedthat R1 and R2 may be an intrinsic part of the data driver bridge.

In summary of FIG. 3, the quality factor of the resonant tank circuit325 is maximized during power transmission, but is purposely loweredduring data transmission (i.e.,Q_(ext_data_timeslot)<Q_(ext_power_timeslot)). The dampened externalresonant tank circuit 325 reduces the ringing effects during one or more‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOKmodulation at f₀. The series resistors 358 and 362 operate to dampen theexternal resonant tank circuit 325 when connected in series between thebetween the driver bridge 340 and the external coil 322.

FIG. 3 also illustrates an implantable receiver circuit 380 configuredto receive separate power and data signals transmitted by the externaltransmitter circuit 320. The implantable receiver circuit 380 comprisesan implantable coil 382 that is part of an implantable (internal)resonant tank circuit 385 that also comprises capacitor 394 (capacitorC4) and capacitor 396 (capacitor C5). In practice, implantable coil 382has an inductive component (LI_(PC)) 377 and some small copper lossesrepresented as the series resistive component (RI_(PC)) 379. Theimplantable receiver circuit 380 also comprises a data output 381, aload 383 (i.e., battery or other energy storage device), and an energyrectifier connected between the implantable coil 382 and the load 383.In certain embodiments, the energy rectifier 384 is a diode.

The implantable receiver circuit 380 is described in relation toexternal transmitter circuit 320. It is to be appreciated that theimplantable receiver circuit 380, or variants thereof, may be used withthe other external transmitter circuits described herein.

Returning to the embodiment of FIG. 3, it has also been discovered thatthe data integrity improves and that the current through external coil322 drops when the external resonant tank circuit 325 is tuned lowerthan the operating frequency. The lower the tuning frequency of theexternal coil 322 is relative to the operating frequency, the higher thedecrease in current flow through the external coil 322 when the driverbridge 340 is acting as a pulsating voltage source. In one example, theoperating frequency of the external coil 322 is 5 MHz and the resonantfrequency of the external resonant tank circuit 325 during datatransmission (f_(res_data_timeslot)) is set equal to 4.75 MHz). Theseries inductors 360 and 364 operate to reduce the resonant frequency ofthe external resonant tank circuit 325 when connected in series betweenthe between the driver bridge 340 and the external coil 322.

The decrease in the external coil current in response to the detuning ofthe resonant frequency prevents interference of the implantablecomponent load 383 with the data recovery at the implantable receivercircuit 380. More specifically, the detuning lowers the peak amplitudeof the data signals so that the diode 384 is maintained in reversepolarization (i.e., non-conducting during data transmission), therebypreventing the load 383 from being seen at the data output 381.

In certain embodiments, the driver bridge 341 is constructed as a fullH-bridge driver, while the driver bridge 340 is a half H-bridge driver.The use of a half H-bridge driver lowers the peak amplitude of the datasignal, thereby assisting in maintaining the diode 384 in reversepolarization. Fine adjustments to the received implant voltage level mayalso be accomplished by altering the pulse width of each RF cycle duringthe data and power time slot or adapting the driver bridge supplyvoltages.

FIG. 4 is a diagram illustrating the signal observed at the implantablereceiver circuit 380 during power time slots 335 and data time slots337. In the illustrative example of FIG. 4, the power time slots 335 areapproximately 0.5 milliseconds (ms) in length, while the data time slotsare approximately 1.5 ms in length (i.e., the power time slots 335occupy approximately ¼ of the time while the data time slots 337 occupyapproximately ¾ of the time).

The implant voltage (VDD) at load 383 is represented in FIG. 4 as dottedline 386. As shown, during the power time slots 335, the implantablereceiver circuit 380 receives all ‘1’ signals. As a power time slot 335ends and a subsequent data time slot 335 begins, ringing is observed atthe implantable receiver circuit 380. This ringing is a result of thehigh quality factor and efficiency of the external resonant tank circuit325 during transmission of the power signals 388. During the data timeslots 335, the ringing is eliminated by reducing the quality factor ofthe external resonant tank circuit 325.

As described above, the peak amplitude of the data signals 410 isreduced from the peak amplitude of the power signals 408. As shown inFIG. 4, the peak amplitude of the data signals 410 is reduced so as tostay below the implant voltage 486 so that the implant voltage is notobserved during the data time slots 337 (i.e., so that the diode 384remains in reverse polarization).

It is to be appreciated that the data time slots 337 may not be fullyfilled (i.e., the number of signals sent may depend on the amount ofdata that needs to be transferred from the external component to theimplantable component). In certain embodiments, all or part of a datatime slot 337 may be used for backlink telemetry where data is sent fromthe implantable component to the external component. As such, theexternal transmitter circuit 320 and the implantable receiver circuit380 are, in practice, both transceiver circuits.

FIG. 5 is a schematic diagram illustrating another external transmittercircuit 520 configured to separately transfer power and data signals toan implantable component via a single external coil 522 in accordancewith embodiments presented herein. Similar to the embodiment of FIG. 3,the external transmitter circuit 520 uses dedicated driver bridges foreach of data and power transmission (i.e., the data and power signalshave their own driver bridges and only a single driver bridge is enabledat a time). However, as described further below, the separate driverbridges are driven differently than as shown in FIG. 3.

In the embodiment of FIG. 5, the external transmitter circuit 520comprises a first driver bridge 540 (data driver bridge) and a seconddriver bridge 541 (power driver bridge) that are each separatelyconnected to the external coil 522. The external coil 522 is part of anexternal resonant tank circuit 525 that also comprises capacitor 542(capacitor C1) and capacitor 544 (capacitor C2). In practice, externalcoil 522 has an inductive component (L_(HPC)) 546 and some small copperlosses represented as the series resistive component (R_(HPC)) 548.

The driver bridge 540 includes an input 550 that receives an inputsignal 531 via input signal line 552 and an enable input 553 thatreceives an enable signal 529 via enable signal line 555. As describedfurther below, the enable input 553 is an inverting input.

The driver bridge 540 also comprises a first output 554 and a secondoutput 556. The first output 554 is connected to capacitor 542 (which isconnected to external coil 522) via a series circuit 557 that comprisesa resistor 558 (R1) in series with an inductor 560 (L1). The secondoutput 556 is connected to capacitor 544 (which is also connected toexternal coil 522) via a series circuit 561 that comprises resistor 562(R2) in series with an inductor 564 (L2).

The driver bridge 541 includes an input 569 that receives the signal 531via input line 552. The driver bridge 541 also comprises an enable input573 configured to receive the enable signal 529 via enable signal line555. In other words, the driver bridge 541 is connected to the sameinput signal line and the same enable signal as the driver bridge 540.The driver bridge 541 also comprises a first output 574 and a secondoutput 576. The first output 574 is directly connected to capacitor 542(which is connected to external coil 522) so as to bypass series circuit557. Similarly, the second output 576 is directly connected to capacitor544 so as to bypass series circuit 561.

In the embodiment of FIG. 5, power and data are transmitted duringnon-overlapping and separate (i.e., different) time slots using theseparate driver bridges 540 and 541. As shown, the input signal 531 is aseries of all ‘1’ values or consecutive RF cycles during a power timeslot 535. However, during a data time slot 537, the input signal 531switches between ‘1s’ and ‘0s’ (i.e., is a digital code representing theOOK modulation). The enable signal 529 is a logic signal thatalternatives between a value of ‘1’ and ‘0.’ The enable signal 529 has avale of ‘1’ during the power time slots 535 and a value of ‘0’ duringthe data time slots 537.

Additionally, during the power time slots, the enable signal 529 is high(i.e., a ‘1’ value) so as to enable driver bridge 541. As such, theoutputs 574 and 576, generated using input signal 531, are used to driveexternal coil 522. As noted, the input 553 of driver bridge 540 is aninverting input. Therefore, when the enable signal 529 is high, theinverting input 553 will cause the driver bridge 540 to interpret theenable signal 529 as low (i.e., ‘0’ value). This causes the outputs 554and 556 of driver bridge 540 to be placed in a high impedance state.

During the data time slots, the enable signal 529 is low so as to causethe outputs 574 and 576 of driver bridge 541 to be placed in a highimpedance state. However, when the enable signal 529 is low, theinverting input 553 will cause the driver bridge 540 to interpret theenable signal 529 as a high value. As such, the outputs 554 and 556,generated using input signal 531, are used to drive external coil 522.

As noted above, the first output 554 is connected to external coil 522via series circuit 557 (R1 and L1) and the second output 556 isconnected to external coil 522 via series circuit 561 (R2 and L2). Assuch, when driver bridge 540 is enabled, the external coil 522 is drivenwith signals that pass through series circuit 557 and series circuit561.

Maximum power efficiency is obtained when the quality factor of theexternal resonant tank circuit 525 during the power time slot ismaximized or RHPC is minimized. Additionally, the external coil currentis maximized when the resonant frequency of the resonant tank circuit525 during the power time slot is substantially equal or close to theoperating frequency (f₀) of the external coil 522. Therefore, as notedabove, during the power time slots, the bridge 541 is enabled to drivethe external coil 522 with signals that pass directly from the outputs574 and 576 to capacitors 542 and 544, respectively. In thisarrangement, the signals bypass the series circuits 557 (R1 and L1) and561 (R2 and L2), thereby ensuring that the quality factor and resonantfrequency of the external resonant tank circuit 525 are not affected bythe series circuits 557 and 561.

However, the data integrity improves when the external resonant tankcircuit 525 is more dampened (i.e., has a lower quality factor) duringdata transmission. As such, during the data time slots, the driverbridge 350 is enabled so as to drive external coil 522 with signals thatpass through the series circuit 557 (R1 and L1) and series circuit 561(R2 and L2). That is, the series circuit 557 (R1 and L1) and seriescircuit 561 (R2 and L2) are placed in between the driver bridge 540 andthe external coil 522. Driving the external coil 522 via the seriescircuits 557 and 561 causes a drop in (i.e., damp) the quality factor ofthe resonant tank circuit 525, the external coil current, and theresonance frequency.

In summary of FIG. 5, the quality factor of the resonant tank circuit525 is maximized during power transmission, but is purposely loweredduring data transmission (i.e.,Q_(ext_data_timeslot)<Q_(ext_power_timeslot)). The dampened externalresonant tank circuit 525 reduces the ringing effects during one or more‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOKmodulation at f₀. The series resistors 558 and 562 operate to dampen theexternal resonant tank circuit 525 when connected in series between thebetween the driver bridge 540 and the external coil 522.

Additionally, it has also been discovered that the external coil currentdrops during the data time slot when the external resonant tank circuit525 is tuned lower than the operating frequency. The lower the tuningfrequency of the external coil 522 is relative to the operatingfrequency, the higher the decrease in current flow through the externalcoil 522 when the driver bridge 540 is acting as a pulsating voltagesource. As described elsewhere herein, the decrease in the external coilcurrent prevents interference of the implantable component load with thedata recovery at the implantable component. In one example, theoperating frequency of the external coil 522 is 5 MHz and the resonantfrequency of the external resonant tank circuit 525 during datatransmission (f_(res_data_timeslot)) is set equal to 4.75 MHz). Theseries inductors 560 and 564 operate to reduce the resonant frequency ofthe external resonant tank circuit 525 when connected in series betweenthe between the driver bridge 540 and the external coil 522.

FIG. 6 is simplified schematic diagram illustrating another externaltransmitter circuit 620 configured to separately transfer power and datasignals to an implantable component via a single external coil 622 inaccordance with embodiments presented herein. Similar to the embodimentof FIG. 5, the external transmitter circuit 620 uses dedicated driverbridges for each of data and power transmission. However, in theembodiment of FIG. 6, two (2) bridges are dedicated for use during powertime slots, while a single separate driver bridge is used during thedata time slots.

The external transmitter circuit 620 comprises a data driver bridge 640and two power driver bridges 641(1) and 641(2). The external coil 622 ispart of an external resonant tank circuit 625 that comprises capacitors642 (capacitors C1, C2, and C3). The driver bridges 640, 641(1), and641(2) receive an input signal 531 (described above with reference toFIG. 5) and an enable signal 529 (also described above with reference toFIG. 5). The enable signal 529 is inverted before reaching data bridge640. The driver bridge 640 may be a half H-bridge driver, while thedriver bridges 641(1) and 641(2) may be full H-bridge drivers.

During the power time slot 535 (FIG. 5), the full H-bridge drivers641(1) and 641(2) are activated and the outputs of the full H-bridgedrivers are used to drive the external coil 622. At the same time, dueto the inversion of the enable signal 529, the half H-bridge driver 640is deactivated and the outputs of the half H-bridge driver are placed ina high impedance state. Placing the full H-bridge drivers 641(1) and641(2) in parallel to operate simultaneously lowers the conductivelosses at the output (relative to a single driver arrangement), therebyfurther increasing the quality factor of the tank circuit.

During the data time slot 537 (FIG. 5) the half H-bridge driver 640 isactivated and the outputs of the half H-bridge driver are used to drivethe external coil 622. As shown in FIG. 6, a resistor 658 and aninductor 660 are connected between the outputs of the half H-bridgedriver 640 and the external coil 622. The positioning of the resistor658 and an inductor 660 between the half H-bridge driver 640 and theexternal coil 622 during data transmission will (1) dampen the resonanttank circuit 625 as described above and (2) lower the signal level ofthe data pulses received by the implant resulting in a non-conductingenergy rectifier as described above.

As noted, backlink telemetry is possible in accordance with embodimentspresented herein. FIG. 6 illustrates a switch 605 that is closed whendata is received at the external transmitter circuit 620 from animplantable component. In essence, the switch 605 bypasses theunidirectional driver bridges 640, 641(1), and 641(2) during backlinktelemetry. Similar switches may be present in the embodiments of FIGS.2A, 3, 4, and 5, but have been omitted from those FIGS. for ease ofillustration.

In summary of FIG. 6, the quality factor of the resonant tank circuit625 is maximized during power transmission because the outputs of thefull H-bridge drivers 641(1) and 641(2) are directly connected to theresonant tank circuit 625. However, the quality factor of the resonanttank circuit 625 is purposely lowered during data transmission. Thedampened external resonant tank circuit 625 reduces the ringing effectsduring one or more ‘0’ cycle transitions after a sequence of ‘1’ cyclesduring use of OOK modulation at L. The resistor 658 operates to dampenthe external resonant tank circuit 625 when connected in series betweenthe between the driver bridge 640 and the external coil 622.

Additionally, the external resonant tank circuit 625 is tuned lower thanthe operating frequency. As described elsewhere herein, the decrease inthe external coil current prevents interference of the implantablecomponent load with the data recovery at the implantable component. Inone example, the operating frequency of the external coil 622 is 5 MHzand the resonant frequency of the external resonant tank circuit 625during data transmission (f_(res_data_timeslot)) is set equal to 4.75MHz). The inductor 660 operates to reduce the resonant frequency of theexternal resonant tank circuit 625 when connected in series between thebetween the driver bridge 640 and the external coil 622.

Embodiments have been primarily described above with reference toadjustments to the operational characteristics of an external resonanttank circuit. However, it is to be appreciated that adjustments to theoperational characteristics of an implantable (internal) resonant tankcircuit may be made in addition to, or in place of, the aboveadjustments to an external resonant tank circuit during the separatedpower and data transfer techniques.

More specifically, FIG. 7 illustrates an implantable receiver circuit780 configured to receive separate power and data signals transmitted byan external transmitter circuit (not shown). The implantable receivercircuit 780 comprises an implantable coil 782 that is part of animplantable (internal) resonant tank circuit 785 that also comprisescapacitor 794 (capacitor C4) and capacitor 796 (capacitor C5). Inpractice, implantable coil 792 has an inductive component (LI_(PC)) 777and some small copper losses represented as the series resistivecomponent (RI_(PC)) 779. The implantable receiver circuit 780 alsocomprises a data output 781, a load 783 (i.e., battery or other energystorage device) connected between a power terminal 785 and a groundterminal 787, and an energy rectifier 784 connected between theimplantable coil 782 and the load 783. In certain embodiments, theenergy rectifier 784 is a diode.

The implantable receiver circuit 780 also comprises a resistor 798 and aswitch 799 connected in parallel to the capacitor 794. During a datatime slot (i.e., when data is received at the implantable coil 782), theswitch 799 is closed. When the switch 799 is closed, the resistor 798 isconnected to the implantable resonant tank circuit 785. The resistor 798operates to dampen the implantable resonant tank circuit 785. In otherwords, the resistor 798 functions to reduce the quality factor of theimplantable resonant tank circuit 785 during data reception.

In certain embodiments, a method for transmitting power from an externaltransmitter circuit to an implantable receiver circuit is provided. Theexternal transmitter circuit comprises an external resonant circuit thatincludes an external coil, while the implantable receiver circuitcomprise an implantable resonant circuit that includes an implantablecoil. The method comprises driving the external resonant circuit withone or more driver bridges during a power time slot to cause theexternal coil to transfer power to the implantable receiver circuit. Themethod further comprises driving the external resonant circuit with oneor more driver bridges during a data time slot to cause the externalcoil to transfer data to the implantable receiver circuit. The power anddata time slots are different time slots and the external resonantcircuit is driven such that the quality factor of the external resonantcircuit is lower during the data slot than during the power time slot.In certain examples, the the external resonant circuit and theimplantable resonant circuit are resonant tank circuits.

In certain examples, the method further comprises driving the externalresonant circuit with one or more driver bridges during the data timeslot such that a resonance frequency of the external resonant circuit isadjusted during the data time slot so as to be lower or higher than theresonant frequency of the external circuit during the power time slots.In further examples, the method further comprises driving the externalresonant circuit with one or more driver bridges during the data timeslot such that a peak amplitude of current used to drive the externalcoil during the data time slots is lower than a peak amplitude ofcurrent used to drive the external coil during the power time slots.

In other examples, the implantable receiver circuit comprises an energyrectifier and the method further comprises driving the external resonantcircuit with one or more driver bridges during the data time slot suchthat the peak amplitude of current used to drive the external during thedata time slot is such that the energy rectifier does not allow currentto pass there through during the data time slots.

As noted above, presented herein are techniques to separately transferpower and data from an external device to an implantable component usinga single external coil and a single implantable coil. The external coilis part of an external resonant tank circuit, while the implantable coilis part of an implantable resonant tank circuit. The external coil isconfigured to transcutaneously transfer power and data to theimplantable coil using separate power and data time slots. At least oneof the external or internal resonant tank circuit is substantially moredamped during the data time slot than during the power time slot.

The techniques presented herein provide high efficiency power transfers(e.g., 40% efficiency over a 12 mm thick skin flap thickness) withoutaffecting the data integrity. High efficiently power transfers mayreduce the number of implantable batteries needed, increase autonomy ofthe implantable component, and enable use of implantable components withlarger skin flaps

In certain embodiments, the data link can be considered as a MagneticInduction (MI) radio system over, for example, 5 MHz and could acceptdata from the bilateral implant during the data time slot. Additionally,ringing effects are substantially eliminated during data transfer due tothe damped external tank circuit. The techniques presented herein mayalso provide stable waveforms shapes during data time slots received bythe implant and almost independent of coupling factor, implant load,data time slot duration or frame occupation.

In certain embodiments, the data link can support other modulationtypes. As amplitude ringing is a phenomena typically observed in OOKmodulation other modulation types such as FSK or PSK may also sufferfrom excessive phase ringing or distortion due to insufficient dampeningduring the data time slot.

The invention described and claimed herein is not to be limited in scopeby the specific preferred embodiments herein disclosed, since theseembodiments are intended as illustrations, and not limitations, ofseveral aspects of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

What is claimed is:
 1. An apparatus, comprising: an external resonant circuit comprising an external coil; and one or more driver bridges configured to cause the external coil to transfer power and data to an implantable receiver circuit using separate power and data time slots, wherein the quality factor of the external resonant circuit is lower during the data slots than during the power time slots.
 2. The apparatus of claim 1, wherein the external resonant circuit is a resonant tank circuit.
 3. The apparatus of claim 1, wherein a resonance frequency of the external resonant circuit is adjusted during the data time slot so as to be lower or higher than the resonant frequency of the external circuit during the power time slots.
 4. The apparatus of claim 3, wherein the resonance frequency of the external resonant circuit is adjusted during the data time slots by selectively adding one or more inductive or capacitive components to the external resonant tank circuit.
 5. The apparatus of claim 4, wherein the resonance frequency of the external resonant circuit is adjusted during the data time slots by selectively connecting one or more inductors, in series, between the one or more driver bridges and the external coil.
 6. The apparatus of claim 3, wherein the resonance frequency of the external resonant circuit is adjusted during the data time slots by selectively removing one or more inductive or capacitive components from the external resonant tank circuit.
 7. The apparatus of claim 1, wherein a peak amplitude of current used to drive the external coil during the data time slots is lower than a peak amplitude of current used to drive the external coil during the power time slots.
 8. The apparatus of claim 7, wherein the implantable receiver circuit comprises an energy rectifier, and wherein the peak amplitude of current used to drive the external during the data time slot is such that the energy rectifier does not allow current to pass there through during the data time slots.
 9. The apparatus of claim 1, wherein the one or more driver bridges comprises a single driver bridge that is used to drive the external coil during both the power and data time slots.
 10. The apparatus of claim 1, wherein the one or more driver bridges comprise at least one data driver bridge that is used to drive the external coil during the data time slots and at least one power driver bridge that is used to drive the external coil during the power time slots.
 11. The apparatus of claim 10, further comprising: a first series circuit comprising a first resistor and a first inductor connected between a first output of the at least one data driver bridge and the external resonant circuit; a second series circuit comprising a second resistor and a second inductor connected between a second output of the at least one data driver bridge and the external resonant circuit; and wherein the at least one power driver bridge is directly connected to the external resonant circuit so as to bypass the first and second series circuits.
 12. The apparatus of claim 11, wherein during the data time slots the at least one data driver bridge is enabled and outputs of the at least one power driver bridge are placed in a high impedance state and wherein during the power time slots the at least one power driver bridge is enabled and outputs of the at least one data driver bridge are placed in a high impedance state.
 13. The apparatus of claim 12, wherein the at least one power driver bridge comprises first and second power driver bridges configured to be simultaneously enabled.
 14. The apparatus of claim 1, wherein the one or more drivers comprise a first dedicated driver bridge that is used to drive the external coil during the data time slots and a second dedicated driver bridge that is used to drive the external coil during the power time slots.
 15. An apparatus, comprising: an implantable resonant circuit comprising an implantable coil; and an external resonant circuit comprising an external coil forming a transcutaneous power and data link with the implantable coil; and at least one driver bridge configured to drive the external coil so as to separately transfer power and data to the implantable coil, wherein operational characteristics of at least one of the implantable resonant circuit or the external resonant circuit are dynamically adjusted during transfer of data to the implantable coil.
 16. The apparatus of claim 15, wherein the external resonant circuit and the implantable resonant circuits are resonant tank circuits.
 17. The apparatus of claim 15, wherein the quality factor of the external resonant circuit is lower during the transfer of data than during the transfer of power.
 18. The apparatus of claim 15, wherein a resonance frequency of the external resonant circuit is adjusted during the transfer of data so as to be lower or higher than the resonant frequency of the external circuit during the transfer of power.
 19. The apparatus of claim 18, wherein the resonance frequency of the external resonant circuit is adjusted during the transfer of data by selectively adding one or more inductive components or capacitive components to the resonant tank circuit.
 20. The apparatus of claim 15, wherein the external resonant circuit is connected to at least one data driver bridge that is used to drive the external coil during the transfer of data and at least one power driver bridge that is used to drive the external coil during the transfer of power.
 21. The apparatus of claim 20, further comprising: a first series circuit comprising a first resistor and a first inductor connected between a first output of the at least one data driver bridge and the external resonant circuit; a second series circuit comprising a second resistor and a second inductor connected between a second output of the at least one data driver bridge and the external resonant circuit; and wherein the at least one power driver bridge is directly connected to the external resonant circuit so as to bypass the first and second series circuits.
 22. The apparatus of claim 21, wherein during the transfer of data the at least one data driver bridge is enabled and outputs of the at least one power driver bridge are placed in a high impedance state and wherein during the transfer of power the at least one power driver bridge is enabled and outputs of the data driver bridge are placed in a high impedance state.
 23. The apparatus of claim 21, wherein the at least one power driver bridge comprises first and second power driver bridges configured to be simultaneously enabled.
 24. The apparatus of claim 15, further comprising: a capacitor connected to the implantable coil and forming part of the implantable resonant circuit; and a resistor connectable in parallel to the capacitor via an implantable switch, wherein during the transfer of data the implantable switch is closed so as to connect the resistor to the implantable resonant circuit to reduce the quality factor of the implantable resonant circuit, and wherein during the transfer of power the implantable switch is opened so as to disconnect the resistor from the implantable resonant circuit. 